1. Field of the Invention
The present invention relates to a mold-type semiconductor device for power rectifying and, more particularly to a semiconductor device constituting a bridge circuit.
2. Description of the Related Art
In a mold-type semiconductor device for power rectifying in which a bridge circuit is used, the bridge circuit, which is formed of the so-called Mesa-type diode or a Planer-type diode, is used. Regarding its assembly system, a method using a lead frame has been employed after many changes. Such a mold-type semiconductor device for power rectifying will be explained with reference to FIG. 1 (perspective view), FIG. 2 (cross sectional view taken along lines A--A of FIG. 1), FIG. 3 (cross sectional view showing the structure of a semiconductor element) and FIG. 9 showing a bridge circuit. In other words, a planer-type or a mesa-type diode, which is used as a semiconductor element constituting the bridge circuit, is applied.
The planer type, which is shown in FIG. 3, will be explained. N- and P-type impurity regions 1 and 2, which show an opposite polarity necessary for the diode, are formed in a silicon semiconductor substrate (not shown) constituting a semiconductor element. Moreover, an N.sup.+ region 3 is described. The N.sup.+ region 3 serves as an isolation region, which is necessary for forming a number of planer-type semiconductor elements in the semiconductor substrate. Also, in the N.sup.+ region 3, a braking process is performed along a dicing line (not shown), which is formed in N.sup.+ region 3, thereby forming an individual semiconductor element.
As shown in the drawing, conductive metal layers 4 and 5 are coated on P.sup.+ region 2 and N.sup.+ region 3, thereby forming electrode layers 4 and 5. In addition, thermal oxidation film 6 is coated by normal thermal oxidation method, thereafter a patterning is performed by a photolithography. Moreover, junction end portions 7 and 8 are exposed to the surface of the semiconductor substrate.
The mesa-type semiconductor element features junction end portions (not shown) which are exposed to the mesa-shaped portion. In other words, an inclined surface, which has a positive bevel in the direction of the thickness of the semiconductor substrate, a negative bevel, or both bevels, is formed by mechanical means, chemical means, or means combining both means. Then, the junction end portions, which are exposed to the inclined surface and which are indispensable for the diode, are normally coated and protected with an encape material such as silicon rubber.
The mold-type semiconductor device, which constitutes a bridge circuit by a plurality of diodes having the above-mentioned structure, has been on sale. The system using the so-called lead frame is employed as an assembly process. This will be explained with reference to FIG. 1 (perspective view), FIG. 2 (cross sectional view taken along lines A--A of FIG. 1).
A connector 10 is integrally fixed to an inner lead 9 by a solder layer 12. Four planer-type or mesa-type semiconductor elements 13, which are necessary for the bridge circuit, is secured to the connector 10 via the solder layer 12. Moreover, in the connectors 10, 10, to which semiconductor elements 13 are fixed, rear electrodes 5, 5 of the semiconductor elements 13, 13 are fixed to a die stage 15, which is formed in a lead frame 14, via the solder layer 12 to be opposite to each other.
Then, a mold layer is coated by the mold process of the well-known transfer mold method, thereby forming a mold-type semiconductor device for power rectifying.